I've ran a 325lb 8" rear and damping to match with good effect. It was probably not as stiff as you'd think. A setup I tried for a track day with a 275 6" front, but it being a G40 broke its gearbox the day before, and with a new lsd box fitted that night shattered the driveshafts. I got some good mileage in on the known local roads, felt great to chuck about compared to the lighter rates, although not a daily setup, liveable with. Key is in setting the dampers right.